International efforts on materials selection and development related to supercritical water-cooled reactors (SCWRs) have produced a considerable amount of data in the open literature , The majority of these data are on aspects of materials properties such as corrosion, stress corrosion cracking, creep, irradiation damage as well as microstructural degradation under various exposure conditions. These prior efforts are helping guide the current selection of candidate alloys for further, longer-term evaluation. As continuing research on the SCWR advances, gaps and limitations in the published data are being identified. In terms of corrosion properties, these gaps can be seen in several areas, including: 1) the test environment, 2) the physical and chemical severity of the tests conducted as compared with likely reactor service/operating condition, and 3) test methods used. While some of these gaps can be filled readily by the current research projects, in particular those occurring in Generation IV International Forum (GIF) member countries, others require further advances in our understanding of material-environment interactions involving supercritical water. Gaps in advanced test facilities for future research are also becoming evident. Future needs for materials development and suggestions for expanded international collaborations to link with groups working on materials for advanced fossil-fired supercritical water power plants, as well as other GEN IV and fusion reactor designs are summarized.